There are a number of convenient ways to travel around Thailand.  These include

By plane

Travelling by plane has its advantages: it’s faster, easier and more convenient when travelling greater distances. The deregulation of the industry has brought inseveral new operators and with a little research it's possible to fly almostanywhere domestically for a couple of thousand baht.

 
Popular airlines for domestic flights include:

Air Asia has good coverage of international and domestic routes in Thailand and offers heavily discounted tickets if booked well in advance

Bangkok Airways promotes itself as "Asia's Boutique Airline", and has a monopoly on flights to its ownairports at Ko Samui (shared with Thai Airways), Sukhothaiand Trat.

Nok Air began in 2004 with a lurid paints scheme featuring a bird's beak painted on the nose. It is owned mostly by Thai Airways, and competes with Air Asia on price.

One-Two-Go is infamous for their 2007 fatal crash in Phuket, and for their old McDonnell Douglas MD-82 planes. Perhaps one to miss if you’re looking to fly with newer planes.

SGA Airline which  operates jointly with Nok Air is currently the only passenger carrier offering flights between Chiang Mai-Pai, Mae Hong Son, Nan and Chiang Rai.

Thai Airways is the most reliable,frequent, and comfortable Thai airline, but usually more expensive than the other options, though bargains can be had in promotions.

By Train

The State Railway of Thailand (SRT) has a 4000-km network covering most of the country, from Chiang Mai in the north all the way to (and beyond) the Malaysian border in the south. When you compare it to buses, most trains are fairly slow and suffer delays, but safer. You can also pick up fruits, snacks and cooked food from hawkers at most stations.

There are different classes:

First class (chan neung) offers 2-berth sleeping compartments with individually regulated air conditioning that’s available on some trains, but prices are sometimes the same as budget airfares.

Second class (chan song) is a good compromise, costing about the same as 1st class buses and with comparablecomfort. Some 2nd class trains are air-con, others aren't.

Third class (chan saam) is the cheapest way to travel in Thailand, with virtually nominal fares, and can be great fun or agre at pain, depending on your outlook.

Pre-booking is recommended, especially for sleeper berths.

By road

Thailand's roads stand head and shoulder sabove its neighbors Myanmar,Laos and Cambodia, but the driving habits are still quite dangerous.

Drunk driving, speeding and reckless overtaking are depressingly common, and bus and taxi drivers (especially for private companies) work almost inhuman shifts and frequently take drugs to keep themselves awake, with tragic results. It's not uncommon for motorbikes to drive close to the curb on the wrong side of the road.

Death tolls shoot right up around major holidays, especially Songkhran, when bystanders tend to throw water on passing cars and bikes. Many drivers don't use headlights at night, and it’s wise to avoid or minimize overnight travel by road.

Expressways carry tolls, so make sure you have plenty of small change.

By bus

Buses travel throughout the country and the government's BKS (บขส Baw Kaw Saw) is known in English as the Transport Company. It has a terminal in every province of any size. BKS buses are the best option for both price and comfort. They’re also private buses sanctioned by BKS, which operate on the same routes from the same terminals with the same fares - these are also fine. The ones to look out for are the illegal bus companies, which operate from tourist areas.

By taxi

Metered taxis are common in Bangkok and become more popular in Chiang Mai,but are rare elsewhere. When available, they are an excellent means of transport - but insist on the meter. Avoid taxis which hang around touristy areas and wait for people. They’re looking for tourists who will take their taxi without using a meter. Always use the meter!